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A249780 Product of lowest and highest prime factors of 2^n-1 2
9, 49, 15, 961, 21, 16129, 51, 511, 93, 2047, 39, 67092481, 381, 1057, 771, 17179607041, 219, 274876858369, 123, 2359, 2049, 8388607, 723, 55831, 24573, 1838599, 381, 486737, 993, 4611686014132420609, 196611, 4196353, 393213, 3810551, 327, 137438953471, 1572861, 849583, 185043 (list; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Chai Wah Wu, Table of n, a(n) for n = 2..200

FORMULA

a(n) = A005420(n) * A049479(n)

EXAMPLE

The lowest and higest prime factors of 2^6-1 are 3 and 7, so A(6) = 21

MAPLE

a:= proc(n) local F; F:= numtheory:-factorset(2^n-1); min(F)*max(F) end proc:

seq(a(n), n=2..50); # Robert Israel, Nov 05 2014

PROG

(PARI) for(n=2, 50, p=2^n-1; print1(factor(p)[1, 1]*factor(p)[#factor(p)[, 1], 1], ", ")) \\ Derek Orr, Nov 05 2014

(Python)

from sympy import primefactors

A249780_list, x = [], 1

for n in range(2, 10):

....x = 2*x + 1

....p = primefactors(x)

....A249780_list.append(max(p)*min(p)) # Chai Wah Wu, Nov 05 2014

CROSSREFS

Sequence in context: A179280 A293095 A283092 * A140891 A072461 A181607

Adjacent sequences:  A249777 A249778 A249779 * A249781 A249782 A249783

KEYWORD

nonn

AUTHOR

Jacob Vecht, Nov 05 2014

EXTENSIONS

More terms from Derek Orr, Nov 05 2014

STATUS

approved

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Last modified April 18 08:37 EDT 2019. Contains 322209 sequences. (Running on oeis4.)